Study of the mechanism of action of mung bean nuclease on native, high molecular weight viral DNA will involve characterization of the large fragments with respect to length (by electron microscope), molecular weight (by ultracentrifugation, electrophoresis, viscosimetry, and by end labeling), termination (by labeling termini) and kinetics of formation (viscosimetry). The attempts to identify the excised small fragments will also be made. Sequencing of the termini of the large fragments will be attempted. A study of the enzyme molecule with respect to composition (amino acids and polysaccharide) as well as of the location of the active center (or centers) of two known activities will be made. A nuclease or nucleases from Alcaligenes faecalis that is capable of hydrolyzing its own DNA only after it has been nicked by pancreatic DNase will be isolated and characterized.